The present invention relates to a holder for a tangential chasing tool. Such tools are used for cutting threads. Hereafter the chasing tool will be called "chaser".
It is required to align or adjust the chaser in its holder to an angular tolerance within the range of about .+-.0.3.degree. relative to the pitch angle of a threading to be cut. The chaser must be clamped tightly in the adjusted position. Therefore, it has been necessary heretofore to provide a plurality of holder sets for one core diameter cutting range. These holder sets divide the sum total of the pitch angles of all standardized threads within said core diameter cutting range and within the above mentioned angular tolerance of about .+-.0.3.degree..
The total range of a thread cutting head thus required heretofore a large number of chaser holders. In order to reduce this large number of chaser holders, it is known from German Patent Publication (DOS) No. 2,626,119 to provide but one chaser holder for one, or rather for each, core diameter cutting range. A set of such holders comprises four holders. Each holder according to said German Patent Publication 2,626,119 is adapted to hold a cassette having a dovetail shaped cross-section. In the cassette, in turn, there are provided the holding means for the tangential chaser. The holding means are also dovetail shaped and arranged at an angle corresponding to the required chaser pitch angle. The respective back surface of the cassette, between the surfaces of the dovetail which are tilted against each other, is milled from both ends. These zones are milled and displaced relative to each other to make the zones elastic and in order to securely clamp the chaser in its cassette as well as the cassette itself. Besides, the back wall of the cassette may also be constructed to be elastic.
The just described device according to said German Patent Publication 2,626,119 achieves a reduction in the number of sets of chaser holders as compared to other prior art structures. Hence costs are reduced, since a cassette is always less expensive than a chaser holder. However, the cassette which encircles the respective chaser dovetail, calls for a substantially wider and deeper chaser seat in the chaser holder as compared to a chaser seat required to hold only the dovetail of the chaser rather than the cassette with a chaser dovetail therein. Thus, the chaser holder constructed for holding a cassette must be made substantially larger than heretofore, if it is required that the holder has the same stiffness as ordinary holders. Besides, cassette holders make it necessary to position the chaser adjustment screw into a pulpit member which reaches above the cassette and which initially does not constitute an integral structure with the chase holder. The pulpit member is subsequently installed and anchored in the chaser holder which itself requires much space. Thus, the structure of the chaser holder becomes even more bulky. Consequently, only a minor fraction of the originally expected savings is actually achieved.
A device for adjusting the pitch angle of the tangential cutting jaws of a thread cutter head is also known in the art. Said device uses sets of intermediate layers or washers inserted into the grooves for the cutting jaws. These intermediate layers or washers have a support surface which is inclined crosswise where the respective angle of inclination corresponds to the pitch angle. However, the cutting jaws does not rest rigidly in the holder, because the groove for the supporting of a clamping iron, which holds a cutting jaw, always has the same inclination and therefore the clamping iron does not rest with a surface and/or in the groove, when different intermediate layers or washers are used.